Drawing ASTs for expressions: Correct Solution

For each of the Java expressions below:

• Draw an AST for the expression.
• Show how the expression evaluates at each node in the tree.

Be sure that your tree accurately reflects how Java would evaluate the expression.

Part 1

Given the following variables:

double rosh = 2.0;
double purnork = 2.0;

...draw the AST and evaluation results for the following expression:

9 % 5 % (9 % 1 - rosh * 9) - purnork * 2

Solution

Things to double-check in your solution:

• Do you have the left and right branches on the correct side?
• Did you indicate the difference between ints and floating point values?

Part 2

Given the following variables:

boolean groba = false;
double er = 3.0;
boolean un = true;
int a = 4;
double bissod = 1.0;
boolean cror = true;

...draw the AST and evaluation results for the following expression:

groba != (8 == er) && un || 9 != a || 4 == bissod == (6 == 3) && cror

Solution

Things to double-check in your solution:

• Does your tree correctly reflect the precedence of && and ||?
• Did you correctly show short-circuiting? (That is when the right branch of && or || is never evaluated because the left branch already determines the answer.)

Part 3

Draw the AST and evaluation results for the following expression:

0 + 1 + (2 + 3 + 4 + 5 + 6 + "7") + "8"

Solution

Things to double-check in your solution:

• Did you indicate the distinction between ints and Strings?
• Are your left/right branches correct?

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